1. Fields of the Invention
The present invention relates to a monitoring system for riverbed elevation monitoring at bridge piers, especially to a probe monitoring system for riverbed elevation monitoring at bridge piers.
2. Descriptions of Related Art
In recent years, natural disasters such as storms and associated flooding become more frequent and severe in countries all over the world. When the disaster comes, it causes serious flooding on the rivers and other streams so that the scour of the bridge foundations is becoming worse and this leads to exposure of bridge foundations. Thus the lateral load acting on the bridge pier is insufficient and the bridge may be tilted or broken. Once the flooding is too vast, the pier is washed away, the bridge collapses and people passing through the bridge may fall into the water. The above condition not only results in traffic interruption, but also great damages to human lives, common property and local construction. Now in order to observe the riverbed scour at bridge piers and make an alarm, a monitor system is developed. Thus the riverbed scour at bridge piers can be found as early as possible so as to assure the bridge safety and provide a precaution alarm. The traffic safety is ensured and the secondary damage caused by the broken bridge can be avoided. Moreover, the lifetime of the bridge is also extended by strengthening and repair taken in time. Furthermore, by long-term record of monitor data, a complete database of the bridge pier scour is established for bridge pier protection and riverbed restoration in the future.
Among a lot of technologies that monitor the bridge pier scour, the most common methods are followings:
Ground penetrating radar: is a non-destructive method that uses electromagnetic radiation in the high frequency band of the radio spectrum, and detects the reflected signals from subsurface structures. Thus the elevation changes of the riverbed under the water are obtained. The advantage of this method is that the changes in the riverbed elevation can be recorded continuously yet the shortcoming is that the operation is time-consuming and staffs require professional training.
Numbered bricks: a brick array formed by bricks with fixed size and sequential numbers is mounted under the riverbed at the upstream of bridge piers. When a flood comes, the riverbed elevation change is measured by the positions and numbers of the bricks swept away. The disadvantage of the method is that it requires to dig in the riverbed for mounting the brick array and each set of array can be used only once. Moreover, only the scour depth is learned while the sediment deposition is unable to detect.
Sliding magnetic collar: a slide bar with a hollow design is disposed on the surface of a bridge pier and a collar sleeve covers the slide bar. When the flood scours, the collar sleeve moves downward to provide the scour depth of a specific position. A magnetic sensor disposed in the slide bar moves along with the collar sleeve and sends movement signals to externals by wires. The disadvantage of this method is that it only records the scour depth but the sediment deposition is unable to detect.
Outdoor devices that monitor the water level: by an image capture device, an image of the water level is obtained. Then an image preprocessing is performed. That means a series of image processing steps are applied to the image. Then calculate the processed image to get the elevation of the water level. However, this method is not proper for monitoring the pier scour.
Auto-lens monitoring: refer to Taiwanese Pat. App. No. 098131157, a hollow container is embedded into the riverbed at a bridge pier and is fixed at the bridge pier. A photographic equipment for monitoring is mounted in the container and is disposed on a carrier. The carrier is moved vertically under control of a motor so as to monitor the sand scour around. When the bed surface rises due to deposition of sediment or falls due to scouring, a real-time image recognition system is used to detect the bed surface position. Thus either deposition of sediment or scouring can be detected. The disadvantage of this method is the riverbed excavation.
Gravity type scour measuring device: the sand surface falls due to scouring and the detector also falls along with the sand surface due to gravity. The elevation decreasing is measured so as to obtain the scour depth. The shortcoming of the method is the embedding of the measuring device and only the scour is detected. When sediments deposit, it is unable to detect.
Transmitter of scour monitoring for soil layer: a plurality of transmitters is embedded in the soil layer. When the sand surface is scoured to a certain degree, the transmitters are moved or vibrated to send signals so as to obtain the scouring of the sand surface. The disadvantage of the method is that the transmitters need to be mounted into the riverbed and only scouring is detected. As to the sediment being deposited on the riverbed, it just doesn't work.
Optical sensor: a measuring system that detects by fiber bragg grating. Once optical fiber is attached with medium, the refractive index in the optical fiber changes and wavelength shift occurs. Thus the depth of the medium can be estimated. The disadvantage of the method is that the optical fiber requires to be mounted into the riverbed and contact with the water surface or sand. Moreover, the optical fiber is fragile.
The monitor methods available now all have certain limitations in use. Generally, the riverbed is excavated for mounting the monitoring system therein or the monitoring system is disposable, used only once. The excavation and embedding are labor and cost intensive. This may cause damage to the bridge pier structure and affect the bridge safety. Thus how to monitor the riverbed scouring at bridge piers by new methods so as to extend the lifetime of the bridge and reduce the cost required has become an important issue now.
Thus there is a need to find out a new monitoring system for riverbed elevation monitoring at bridge piers that overcomes above shortcomings and monitors the riverbed elevation in real time with reduced cost.